Short‐crested waves in the surf zone

• Published in: Journal of geophysical research. Oceans 2017-05, Vol.122 (5), p.4143-4162
• Main Authors: Wei, Zhangping, Dalrymple, Robert A., Xu, Munan, Garnier, Roland, Derakhti, Morteza
• Format: Article
• Language: English
• Subjects: Amplitude; Beaches; Breakers; Breaking waves; Cells; Circulation; Components; Computational fluid dynamics; Directional spectra; Fluid flow; Geophysics; Hydrodynamics; Interactions; intersecting wave trains; Mathematical models; Meshless methods; Nearshore circulation; Numerical models; Rip currents; Rotation; Scale (ratio); Short-crested waves; Smooth particle hydrodynamics; Spectra; Studies; Superposition (mathematics); Surf; Surf zone; Surface acoustic waves; Undertow; Vertical vorticity; Vortices; Vorticity; vorticity generation; Wave amplitude; wave amplitude diffraction; Wave breaking; Wave crest; Wave crests; Wave diffraction; Wave interactions; Wave packets; Wave spectra; Wave trains; wave‐current interaction
• ISSN: 2169-9275; 2169-9291
• DOI: 10.1002/2016JC012485

This study investigates short‐crested waves in the surf zone by using the mesh‐free Smoothed Particle Hydrodynamics model, GPUSPH. The short‐crested waves are created by generating intersecting wave trains in a numerical wave basin with a beach. We first validate the numerical model for short‐crested waves by comparison with large‐scale laboratory measurements. Then short‐crested wave breaking over a planar beach is studied comprehensively. We observe rip currents as discussed in Dalrymple (1975) and undertow created by synchronous intersecting waves. The wave breaking of the short‐crested wavefield created by the nonlinear superposition of intersecting waves and wave‐current interaction result in the formation of isolated breakers at the ends of breaking wave crests. Wave amplitude diffraction at these isolated breakers gives rise to an increase in the alongshore wave number in the inner surf zone. Moreover, 3‐D vortices and multiple circulation cells with a rotation frequency much lower than the incident wave frequency are observed across the outer surf zone to the beach. Finally, we investigate vertical vorticity generation under short‐crested wave breaking and find that breaking of short‐crested waves generates vorticity as pointed out by Peregrine (1998). Vorticity generation is not only observed under short‐crested waves with a limited number of wave components but also under directional wave spectra. Key Points Short‐crested waves generated by intersecting wave trains are numerically modeled by GPUSPH Wave‐current and wave‐wave interactions drive enhanced wave amplitude diffraction and multiple nearshore circulation cells and vortices Short‐crested wave breaking generates vorticity, verified by waves with a limited number of components, but also directional wave spectra